Maybe he was just caught?
Breh he was asking for it, begging for it. Not only this fight but his whole career leading up to it. Attacking strictly in a straight line, zero fukks given about head movement, he had it coming. When you go 12 with washed ass Arreola and eat tons of punches in the process you already know something isn't right. Helenius tagged him with some nice shots too before the stoppage, Kownacki just walked through it mostly and by the end of the third, it seemed like he's on the cusp of a stoppage win. Only to get caught by better shots.
I'm telling you he is not the kind of fighter ho gonna improve a lot either, he is who he is, found his ceiling and it won't go up.